feat(webui): bootstrap session handling and login process

pkg/webui/error.go

@@ -0,0 +1,21 @@
+package webui
+
+import (
+	"html/template"
+	"net/http"
+)
+
+var errorTemplates = template.Must(template.ParseFS(htmlFS, "html/base.html", "html/error.html"))
+
+func errorResponse(w http.ResponseWriter, status int, err error) {
+	type ErrorData struct {
+		Err        error
+		Status     int
+		StatusText string
+	}
+	render(w, errorTemplates, status, &ErrorData{
+		Err:        err,
+		Status:     status,
+		StatusText: http.StatusText(status),
+	})
+}